1. Field
This disclosure relates to fabrication of semiconductor devices and, more specifically, to the use of masks during the fabrication process, such as masked ion implant process.
2. Related Arts
Typically implanted pattern has stringent requirements for accuracy of features, such as location and spacing of implanted lines. The lines may be, for example, implant for increase conductance under metal fingers used to draw current from solar cells. These lines may be very thin and very dense (i.e., narrow pitch), requiring high accuracy of the implant. Many times more than one implanted pattern is needed on the same substrate. In that case, high level of accuracy needs to be maintained not only in one implant step but through multiple implant steps—sometimes across several processing tools. In order to achieve this, high precision alignment is necessary between the substrate and the patterning mask. Common approach is to precision align the mask and substrate together in vacuum and then implant through the mask. But such an approach has some challenges, including the following. Precision alignment in vacuum environment, optically or by other means, is difficult and very expensive. For multiple implants, precision alignment needs to be repeated multiple times to accommodate each mask change for different patterns. Exchanging masks in vacuum environment adds alignment inaccuracy, cost and complexity.
Accordingly, there is a need in the art for simpler system for alignment of substrates to masks. Generally, any alignment steps that can be performed in atmospheric environment reduce the complexity and cost of the system. Moreover, removing the requirement for precise orientation during the transport of the substrate holder throughout the system would further reduce the complexity and cost of the system.